For example, a gas turbine includes a compressor, a combustor, and a turbine. Air is taken in from an air inlet and compressed by a compressor, and then the air becomes high-temperature and high-pressure compressed air. In the combustor, fuel is supplied to the compressed air to burn the fuel, so that high-temperature and high-pressure combustion gas is obtained. The turbine is then driven by the combustion gas to drive a generator connected to the turbine.
In such a gas turbine combustor, in order to prevent flashback and burnout of wall surfaces, outside air is taken in from an external wall of a combustion chamber positioned near an apical end of a premixing nozzle, and the taken outside air flows along an inner wall surface of the combustion chamber as film air. However, the film air cools the combustion gas quickly in a part-load operation area of the gas turbine in which the temperature of the combustion gas in the combustor is low. Therefore, the timing of burning fuel gas (for example, methane) to cause a chemical reaction from carbon monoxide (CO) to carbon dioxide (CO2) is delayed, and carbon monoxide and unburned hydrocarbon (UHC) may be generated in a large quantity.
As a technique for solving such a problem, for example, there is a technique described in Patent Literature 1 mentioned below. In a gas turbine combustor described in Patent Literature 1, a ring-shaped contraction member in a frustoconical shape is mounted concentrically on an inner cylinder wall at the back of the combustor. Therefore, film air flows toward a central part by the contraction member and is mixed with high-temperature combustion gas to promote a combustion reaction, thereby enabling to suppress generation of carbon monoxide and unburned hydrocarbon.